1. Field Of The Invention
Plastic pipe is commonly used today in gas and water piping systems as well as other industrial applications. Thermoplastic pipe is superior to metal pipe in many applications since it is not subject to rust, corrosion or electrolysis and when buried in the ground it has an exceedingly long life. One of the advantages of the use of plastic pipe is that it can easily be joined end-to-end by heat fusion. That is, the ends of the plastic pipe can be heated and, while in a molten or semi-molten state, forced into contact with each other. When the molten plastic at the ends is allowed to solidify, which takes place rather quickly, the pipe is joined.
Machines for butt fusion of plastic pipe have long been used. A butt fusion machine typically includes a frame that supports a first clamp for holding the end portion of one length of plastic pipe and a second clamp for holding the end portion of a second length of plastic pipe. The second clamp is movable on the machine frame. The pipes to be joined can be clamped into position with their ends spread apart. A platen heating element can be applied to heat the opposed ends of the pipe to fusion temperature. The platen is removed and while the ends are in the molten state, the second clamp is moved to force the ends of the pipe in direct axially aligned contact with each other. The pipes are held in this position until the molten plastic solidifies, thereby joining two lengths of pipe. Usually the movement of the second clamp toward the first clamp is controlled by a manually operated lever or gear. A problem exists in that the amount of force employed in moving the pipes toward each other is controlled by the operator. If too little axial force is applied, a poor bond is obtained with the results that the pipes later separate, particularly when subjected to internal fluid pressure. On the other hand, if too much pressure is applied while the ends are in the fusion state large internal and external beads of molten plastic are formed. The internal beads are particularly undesirable since they restrict the flow of fluid through the pipe and serve to impede passage of any physical object that might be run through the pipe.
2. The Prior Art
Devices for butt fusion of thermoplastic pipe are illustrated and described in the following United States Patents:
______________________________________ U.S. Pat. No. Title Issued ______________________________________ 3,729,360 Portable Thermoplastic Pipe Fusion Apr 24, 1973 apparatus 3,793,119 Facing Tool For Plastic Pipe Fusion Feb 19, 1974 Apparatus 3,846,208 Combination Pipe Fusion Unit Nov 05, 1974 4,310,737 Pipe Resistance Butt Welding Jan 12, 1982 Apparatus 4,352,708 Defined Force Fusion Machine For Oct 05, 1982 Joining Plastic Pipe 4,323,752 Pipe Resistance Butt Welding Apr 06, 1982 Apparatus 4,445,677 Clamping Apparatus For Plastic May 01, 1984 Pipe 4,533,424 Pipe Fusion Apparatus with Load Aug 06, 1985 Cell For Attaching Side Wall Fittings 4,542,892 Poly-Pipe Fusion Machine Sep 24, 1985 4,556,207 Clamping Apparatus For Plastic Dec 03, 1985 Pipe 4,640,732 Apparatus For Fusion Joining Of Feb 03, 1987 Thermoplastic Pipes 4,714,513 Apparatus For Fusion Welding Dec 22, 1987 Plastic Pipe Joints 4,792,374 Apparatus For Fusion Joining Dec 20, 1988 Plastic Pipe 4,927,999 Apparatus For Fusion Joining May 22, 1990 Plastic Pipe 5,013,376 Programmable Computer Controlled May 07, 1991 Pipe Fusion Device ______________________________________
In addition, a machine for butt fusion of pipe that functions as above described has been sold for many years by T. D. Williamson, Inc. of Tulsa, Okla. and identified as the "TD-45 Polyfuse Butt-Fusion Machine." The operation and maintenance manual describing this machine was published in 1990 and shows a machine as above described in which a lever is manually applied to move the pipes toward each other during the butt fusion process. The present disclosure is an improvement in the machine of the type as particularly described in the "TD-45 Polyfuse Butt-Fusion Machine" and wherein, instead of employing a manually operated lever for moving the lengths of pipe into abutting relation for fusion bonding, spring tension is employed.
The use of spring tension helps alleviate variations in the fusion process that occur with manual operation of the butt fusion machine and provides a means of applying more uniform compressive force between the lengths of pipe.